CTHREAD considerations" /> Limitation of concurrent threads

 

Limitation of concurrent threads

The number of tasks accessing the queue manager could also have an impact on performance, particularly if there are other constraints, such as storage, or there are a large number of tasks accessing a few queues. Symptoms of this could be heavy I/O against one or more page sets, or poor response times from tasks known to access the same queues.

There are three parameters specified in the CSQ6SYSP macro that control the number of threads (see the WebSphere MQ for z/OS System Setup Guide for details). These are:

IDFORE

Specifies the number of TSO sessions that can connect to the queue manager concurrently.

IDBACK

Specifies the number of batch tasks (excluding TSO tasks) that can connect to the queue manager.

CTHREAD

Specifies the total number of threads that can connect to the queue manager. This includes batch, TSO, IMS, and CICS.
Notes:

  1. Each CICS region takes up nine of the threads specified here, plus one thread for each task initiator (CKTI).

  2. The channel initiator makes a number of connections to the queue manager that allow for when setting the CTHREAD system parameter. The number of connections is up to eight plus the combined value of the queue manager parameters CHIADAPS and CHIDISPS. These values are queue manager attributes and we can set them using the ALTER QMGR command. See the WebSphere MQ Script (MQSC) Command Reference for more information.

  3. For IMS connections, the number of threads required is one for the control region, and one for each dependent region connected to WebSphere MQ. For each IMS MPP or IFP region that is defined to permit WebSphere MQ connections through either a specific SSM=EXEC parameter or through the control region default, a thread is created when the first application is scheduled in that region, regardless of whether that application invokes any WebSphere MQ calls. The value you set for CTHREAD should take account of this.

We can change the number of threads while a queue manager is running by using the SET SYSTEM command.

In a CICS environment, we can use CICS MAXTASK to limit concurrent access.